Automated robotic measuring system

ABSTRACT

An automated coordinate measuring system comprising a measuring arm used for acquisition of geometry data that incorporates an exoskeletal structure resilient to physical perturbations including thermal changes and vibrations which may affect coordinate data acquisition. The system may be adapted to a portable platform allowing for convenient positioning and alignment of the measuring arm in a wide variety of environments.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/758,697 filed Jan. 14, 2004 entitled “AUTOMATED ROBOTIC MEASURINGSYSTEM,” which is incorporated herein by reference in its entirety. Thisapplication incorporates by reference in its entirety the followingco-pending application: U.S. application Ser. No. 10/758,696 filed Jan.14, 2004 (attorney docket number ROMINC.003A) entitled “TRANSPROJECTIONOF GEOMETRY DATA.”

BACKGROUND

1. Field of the Invention

The present teachings generally relate to rectilinear measuring systemsand articulated arm coordinate measuring machines and more particularlyto a system for automated measuring arm positioning.

2. Description of the Related Art

Rectilinear measuring systems, also referred to as coordinate measuringmachines (CMM's) and articulated arm measuring machines includingportable coordinate measuring machines (PCMM's) have been described forgenerating geometry information from various objects and areas. Ingeneral, these instruments capture the structural characteristics of anobject for use in electronic rendering and duplication. One example of aconventional apparatus used for coordinate data acquisition comprises asupport and a moveable measuring arm made up of hinged segments to whicha contact-sensitive probe or remote scanning device is attached.Geometry information or three-dimensional coordinate data characterizingthe shape, features, and size of the object may be acquired by tracingor scanning along the object's surface and contours. Probe or scanningdevice movement is typically tracked relative to a reference coordinatesystem resulting in a collection of data points and information that maybe used to develop an accurate electronic rendering of the object. Inconventional implementations, the acquired geometry information isprocessed by a computer capable of making use of the information tomodel the surface contours and dimensions of the object.

One limitation of many conventional instruments is that they aregenerally sensitive to external physical perturbations includingvibrations and fluctuations in temperature which may degrade theaccuracy of coordinate acquisition. For example, it may be necessary toperform coordinate calibration processes several times in a particularenvironment where the ambient temperature changes even a few degrees tocompensate for thermal expansion and contraction of joints andcomponents in an instrument. In articulated measuring arms, thecomponents that make up the arm segments and hinged portions of themeasuring arm are particularly susceptible to localized thermal effectsaffecting the performance of the instrument and can impart undesirabledistortions and inaccuracies in coordinate acquisition. Additionally,imperfections in hinge, actuator, and motor design can result in acertain degree of variability or “slop” in measuring arm movementfurther affecting the overall instrument accuracy.

Another problem with existing designs is that inadvertent jarring of theinstrument by an operator or other vibrations may result in degradationof coordination acquisition performance. Consequently, conventionalinstruments must be treated as highly-sensitive pieces of equipment andare generally set up in a controlled environment to insure maximumaccuracy and reliability. Despite these considerations it is notuncommon for an instrument to require realignment or recalibrationduring routine operation thus increasing the time required to obtain acomplete coordinate set for a selected object.

For the aforementioned reasons of environmental sensitivity as well asthe generally large overall size, weight, and complexity of theinstrument itself, conventional instruments are also not well suited foradaptation to portable platforms which include motor-assisted measuringarm articulation or robotic control. Development of a powered means forassisting in measuring arm positioning presents a number of designconsiderations that should be addressed to insure sufficient reliabilityand precision in coordination acquisition. These factors includeevaluating how motors and actuators should be positioned about themeasuring arm to reduce or offset thermal effects as well as consideringhow these components might best be positioned to increase overallstability and reduce vibrations affecting the instrument.

From the foregoing it will be appreciated that there is a need for animproved means of vibration damping and thermal compensation incoordinate acquisition instruments including CMMs and PCMMs.Additionally, there is a need for an instrument platform capable ofmotor-assisted or robotically controllable movement that is relativelyeasy to calibrate and retains a high degree of accuracy and sensitivity.Such an instrument would be of substantial benefit in a number ofdifferent applications and provide increased flexibility overconventional designs.

SUMMARY

The present teachings relate to an articulated arm coordinate measuringmachine (CMM) having improved tolerance to external physicalperturbations. In various embodiments, the CMM comprises a measuring armhaving a coordinate acquisition probe or remote scanning device attachedthereto coupled with a powered exoskeletal frame and other componentsthat provide improved vibration and temperature damping characteristicsover conventional designs.

In one aspect, the exoskeletal frame and other components that make upthe apparatus for actuator assisted movement of the measuring arm may beadapted for use with existing CMM's thus providing a means to improvethe performance of these devices. In another aspect, the presentteachings describe a configuration for a CMM capable of robotic ormotor-assisted movement. Actuators provide movement for the measuringarm and may be remotely located at various positions on the measuringarm or separately contained in an external housing to improve stabilityand coordinate acquisition accuracy. In certain embodiments, theactuators remotely drive selected hinge, joint, or measuring armaturesegments using flexible drive cables which enable multi-axis control andmovement of the measuring arm, probe, and/or remote scanning device.

In still other embodiments, the present teachings describe arobotically-assisted PCMM that may be operated in a power-assistedmanual mode. The PCMM is capable of withstanding various vibrations andjarring effects through a vibration damping system between theexoskeletal frame and the measuring arm. The PCMM may be configured torecognize when the measuring arm has become mispositioned and maycompensate or realign the measuring arm as desired or instructed.

In another aspect, the present teachings describe a system forcalibrating and training a CMM. Calibration may be performed in asubstantially automated manner or alternatively an operator-assistedmode may be used. Once a training parameter set has been developed, thisinformation may be applied to other similar CMMs improving theefficiency of device calibration or substantially eliminating thisprocess altogether.

In other embodiments, the present teachings describe a process fordetermining the position of the measuring arm using encoders whichdetect the angular position of both the measuring arm and theexoskeletal frame relative to one another. Actuator positioninginformation stored in a lookup table in combination with encoderdetermined angular values provides a highly accurate database foraligning the measuring arm and providing feedback to correct/adjust theposition of the measuring arm.

In various embodiments, the invention comprises a positioning system foraccurately orienting an articulated arm. The system further comprises anarticulated supporting arm comprising a plurality of jointedlyinterconnected support arm segments moveable about a plurality of axes;a plurality of compliant members positioned on said supporting arm; andan articulated measuring arm comprising a plurality of jointedlyinterconnected measuring arm segments capable of a plurality of degreesof freedom of movement and supported by said compliant members whereinsaid compliant members provide a yielding characteristic between thearticulated supporting arm and the articulated measuring arm.

In other embodiments, the invention comprises an accurate positioningsystem. The system further comprises an articulated supporting armcomprising a plurality of jointedly interconnected support arm segmentsmoveable about a plurality of axes; a plurality of compliant memberspositioned about said supporting arm; an articulated measuring armcomprising a plurality of jointedly interconnected measuring armsegments capable of a plurality of degrees of freedom of movement andsupported by said compliant members wherein said compliant membersprovide a yielding characteristic between the articulated supporting armand the articulated measuring arm. A controller is further configured todirect positioning of the articulated supporting arm and a datastorecontaining information that is accessible by the controller is used toresolve the alignment of the articulated supporting arm with respect tothe articulated measuring arm.

In still other embodiments, the invention comprises a method forpositioning an articulated measuring arm. The positioning method furthercomprises supporting said arm at a plurality of locations with compliantmembers to reduce mechanical stress on said arm.

In another embodiment, the invention comprises a method for dampingexternal perturbations encountered by an articulated measuring arm. Themethod further comprises supporting said arm at a plurality of locationswith compliant members that position at least a portion of thearticulated measuring arm within an exoskeletal structure.

In yet another embodiment, the invention comprises a method fordirecting positioning of an articulated positioning arm and aninterconnected articulated measuring arm. The method further comprisesthe steps of: (a) identifying a plurality of instructions used by acontroller to direct positioning of the articulated positioning arm in aplurality of orientations; (b) measuring the resulting position of thearticulated measuring arm arising from each controller instruction; and(c) associating and storing the instructions and the resultingpositionings thereafter to be used by the controller to effectuate aselected positioning.

In still other embodiments, the invention comprises a positioning systemfor directing positioning of an articulated arm. The system furthercomprising: an articulated arm comprising jointedly interconnected armsegments moveable about at least one degree of freedom; an articulationmember configured to position the jointedly interconnected arm segments;and a remotely located actuator interconnected to the articulationmember by a drive member, wherein the actuator generates a motive forcetransmitted through the drive member to the articulation memberdirecting positioning by the articulation member and effectuatingmovement of the positioning arm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one embodiment of an automated robotic measuringsystem according to the present teachings.

FIG. 2A illustrates an exemplary articulated measuring arm and ranges ofmovement imparted by various articulation members.

FIG. 2B illustrates an exploded view of a portion of the measuring armshown in FIG. 2A exemplifying the interconnection between inner andouter members.

FIG. 2C illustrates an exemplary encoder arrangement along the measuringarm.

FIG. 3 illustrates an exemplary actuator configuration for the automatedrobotic measuring system.

FIG. 4 illustrates another exemplary actuator configuration for theautomated robotic measuring system.

FIG. 5 illustrates a block diagram of the components that provide forfeedback and control of the automated robotic measuring system.

FIG. 6 illustrates a flowchart for developing a training parameter setfor the automated robotic measuring system.

FIG. 7 illustrates an exemplary lookup table used in conjunction withthe automated robotic measuring system.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

The following detailed description presents various descriptions ofcertain embodiments of the present teachings described herein. However,the inventive scope of the present teachings can be embodied in amultiplicity of different ways as defined and covered by the claims. Inthis description, reference is made to the drawings wherein like partsare designated with like numerals throughout.

While various embodiments of the present teachings are directed towardsan automated robotic measuring system or a motor-assisted coordinatemeasuring machine; one skilled in the technology will appreciate thatthe systems and methods described herein may be adapted for use withother types of CMMs and PCMMs. For example, the vibration damping andthermal compensation features may be adapted for use with conventionaldesigns to improve their resistance to external perturbations.Similarly, the motor-assisted control and movement characteristics ofthe present teachings may be adapted for use with conventional CMMdesigns to improve the precision and accuracy of these assemblies. Itshould be noted that the motor-assisted designs illustrated in the FIGS.1, 3, and 4 are but various representative embodiments of the scope ofthe present teachings. It will be appreciated that the invention is notlimited exclusively to these embodiments, but rather includes additionalimplementations as well.

In various embodiments, the automated robotic measuring system comprisesan “arm within an arm” or dual-positioning member design wherein ameasuring arm to which a coordinate acquisition member or probe isattached is adapted for use with a positioning member comprising a shellor arm alignment structure. In certain embodiments, the positioningmember forms an exoskeletal structure which at least partially enclosesportions of the measuring arm, although the positioning member is notnecessarily limited to this particular configuration.

The measuring arm and positioning member are interconnected by way ofdeformable compliant members or support webs which align the measuringarm and positioning members with respect to one another and aid indetecting loads imparted upon either component. In one aspect, detectedloads serve as a basis for providing power-assisted movement of the armmembers in various controllable manners. The exoskeletal or alignmentstructure further serves as a physical perturbation damping means whichcontributes to improved stability and accuracy of the measuring arm towhich the coordinate acquisition or probe member is attached therebyimproving the performance of the instrument.

As will be described in greater detail hereinbelow, the automatedrobotic measuring system of the present teachings differs fromtraditional or conventional designs in that the first measuring armmember is driven by the positioning member using an actuator andencoder-based control system instead of a robotic system employing asingular arm member designed for both movement and measurement. Thisdifference in design is significant as it increases measuring armstability, allows for finer and more precise movement, and contributesto improved measurement accuracy.

FIG. 1 illustrates an exemplary automated robotic measuring system 100according to the present teachings. The system 100 comprises acoordinate measuring machine having an articulated measuring arm 105 towhich a coordinate acquisition member 110 is mounted. The measuring arm105 is used to align the coordinate acquisition member 110 in variousspatial orientations through a plurality of articulation members 115each of which impart one or more rotational or angular degrees offreedom to the measuring arm 105 to thereby allow fine positioning ofthe coordinate acquisition member 110 in three dimensional space.

In various embodiments, the coordinate acquisition member 110 comprisesa contact sensitive member or probe configured to engage the surfaces ofa selected object and generate coordinate data on the basis of probecontact as directed through the measuring arm 105. Alternatively, thecoordinate acquisition member 110 may comprise a remote scanning anddetection component that does not necessarily require direct contactwith the selected object to acquire geometry data. In the illustratedembodiment, a laser coordinate detection device (e.g. laser camera) maybe used to obtain geometry data without direct object contact. In thepresent teachings, acquisition of coordinate data is generally describedin the context of the laser coordinate detection device; however it willbe appreciated that the system and methods described herein may bereadily adapted to numerous different configurations to achieve othermanners of coordinate data acquisition. Commercial implementations ofcontact sensitive probes and laser coordinate detection devices havebeen described elsewhere and are available from Romer/Cimcore (Carlsbad,Calif.). For example, it will be appreciated that various coordinateacquisition member configurations including: a contact-sensitive probe,a remote-scanning probe, a laser-scanning probe, a probe that uses astrain gauge for contact detection, a probe that uses a pressure sensorfor contact detection, a probe that used an infrared beam forpositioning, and a probe configured to be electrostatically-responsivemay be used for the purposes of coordinate acquisition.

In various embodiments, the measuring arm 105 comprises a compositestructure having a plurality of hingedly connected measuring armsegments each of which comprises inner member measuring arm segments(inner members) 130 and outer member exoskeletal frame positioningsegments (outer members) 132. The inner member measuring arm segments130 are interconnected to one another through swiveling joints andprovide the ability to position the coordinate acquisition member 110 ina variety of different orientations in three dimensional space. Theouter member positioning segments 132 surrounding various portions ofthe inner members 130 form an environmental barrier that substantiallyencloses portions of the inner members 130. In one aspect, the innermembers 130 are configured to “float” inside the outer members 132 withthe outer members 132 providing powered movement to the inner members130.

Spacing and alignment of the inner 130 and outer 132 members isaccomplished by way of a plurality of compliant members 135. Althoughillustrated as substantially enclosing the inner members 130, it will beappreciated that in various embodiments the outer members 132 of theexoskeletal frame may only partially enclose portions of the innermembers 130 of the measuring arm 105 or alternatively may not enclosethe inner members 130 of the measuring arm 105 at all but rather beinterconnected by way of the compliant members 135 in other mannerswherein the outer members 132 of the exoskeletal frame are still able toprovide the desired vibration and thermal damping features described ingreater detail hereinbelow.

In various embodiments, the outer members 132 comprising the exoskeletalframe may be constructed from a variety of materials including forexample: composite materials such as carbon fiber; synthetic plastics orresins; and metals or metal alloys. The exoskeletal frame desirablypossesses physical characteristics which may include sufficient rigidityto retard deformation under load; low thermal expansion properties;relatively light weight; chemical and electromagnetic radiationresistance; vibration damping characteristics and other such properties.In one aspect, the outer members 132 serve as a shell or enclosure forvarious portions of the measuring arm 105 and partially or fully shieldor dampen the inner members 130 against undesirable physicalperturbations including temperature fluctuations and vibrations. Incertain embodiments, the exoskeletal frame may be adapted for use withthe measuring arm of a conventional CMM instrument to desirably impartthe aforementioned features and dampening characteristics.Alternatively, a customized coordinate measuring machine having fullyintegrated inner member measuring arm segments 130 and exoskeletal framepositioning segments 132 may be developed in a variety of differentshapes, sizes, and configurations to accommodate various differentapplications.

In one aspect, the measuring arm 105 may be secured to a support surface137 at its base 140 wherein the support surface 137 represents a stablesurface such as a table, floor, or wall or alternatively the supportsurface 137 may be contained on a mobile unit 145 used for convenientlymoving the measuring arm 105 and associated components from one place toanother. The illustrated mobile unit 145 and associated measuring arm105 represent one possible embodiment of a PCMM 100 in accordance withthe present teachings. Here, the measuring arm 105 may be secured to themobile unit 145 in a fixed manner (e.g. bolted or fastened to the mobileunit 145 at a selected location) or alternatively a rail system 147 maybe incorporated into the mobile unit design allowing the measuring arm105 to be conveniently positioned and secured in a more adjustablemanner by slideable movement along the rail 147 to a desired location.

The mobile unit 145 may further be configured with retractable ordrop-down wheels 150 which facilitate moving the apparatus. Whenproperly positioned, the wheels 150 may be retracted and rigid supportlegs (not shown) may be used to secure the mobile unit 145 in a fixedposition to provide a stable support surface for the measuring arm 105to perform coordinate data acquisition.

In various embodiments, the mobile unit 145 may comprise a cabinethaving sufficient space to store actuators used to position the outermembers 132 as well as other instruments and components associated withthe PCMM 100 such as computers, power supplies, cabling, gears, etc. ThePCMM 100 may additionally incorporate a handle or push-bar assembly 160that facilitates manually moving and positioning the apparatus 100.Alternatively, the mobile unit 145 may include a powered means oflocomotion and steering allowing the PCMM 100 to be remotely controlledand positioned.

The measuring arm 105 and coordinate acquisition member 110 may bemanually, robotically, or semi-robotically operated as will be describedin greater detail hereinbelow adjusting their position and therebyorienting the coordinate acquisition member 110 in various desiredpositions. In various embodiments, the articulation members 115 are notengaged directly via an actuator or motor but rather respond to forceexerted by various outer members 132. The outer members 132 are operatedby transmission of force and/or torque through flexible drive cables 155which allow actuators, motors, or other devices to be remotely locatedrelative to the outer members 132 and associated articulation member(s)115. The drive cables 155, the actuator or other force-generating devicemay be used to direct the positioning of the articulation members 115with a high degree of precision and control as will be described ingreater detail hereinbelow. In general, the actuators or motors are usedto angularly position the outer members 132 which in turn impart amoving force that positions the inner member(s) 130 in a desired manner.

In one aspect, remote positioning of the actuators is desirable as thisallows for the heat and weight associated with the actuators to bedisplaced from the articulation member 115 it is used to drive. Such aconfiguration may also reduce vibrations and reflected load resultingfrom operation of the actuators to improve the overall accuracy andperformance. As will be shown in subsequent illustrations, the actuatorsmay be positioned within the mobile unit 145 to provide a substantiallyself-contained instrument wherein the drive cables 155 extend from themobile unit 145 and are attached to selected outer member aligningcomponents associated with the articulation members 115 of the measuringarm 105. Remote mounting of the actuators in the aforementioned mannerdesirably reduces or eliminates sources of substantial physicalperturbations that might otherwise affect the performance of theinstrument and desirably displaces weight associated with the actuatorsto promote measuring arm stability (e.g. providing a favorable center ofgravity).

FIG. 2A illustrates some of the possible ranges of movement or angulardeflections of the measuring arm 105 imparted by the variousarticulation members 115 which are responsive to movement of the outermembers 132. In one aspect, the measuring arm 105 may be analogized to ahuman arm having a shoulder joint 205, elbow joint 210, and wrist joint215 with interposing measuring arm sections 220 comprising the inner andouter members 130, 132. Together these joints 205, 210, 215 andmeasuring arm sections 220 provide seven rotary axes of movement with anadditional linear axis of movement provided by the aforementioned railsystem 147. It will be appreciated, however, that there is no strictlimitation to the number of axes of movement that may be used and feweror additional axes of movement may be incorporated into the PCMM designwithout departing from the scope of the present teachings.

For the purpose of illustration, a plurality of rotational axes andassociated angular deflections are shown for the various joint elementsof the measuring arm 105. For example, the ‘A’ axis represents arotational degree of freedom about the base portion 140 of the measuringarm 105. In a similar manner, the ‘B’ axis represents a rotationaldegree of freedom about the shoulder joint 205. The ‘C’ axis representsa rotational degree of freedom about the shoulder/elbow section. The ‘D’axis represents a rotational degree of freedom about the elbow joint210. The ‘E’ axis represents a rotational degree of freedom about theelbow/wrist section 220. The ‘F’ axis represents rotational degree offreedom about the wrist joint 215. Finally, the ‘G’ axis represents arotational degree of freedom about the coordinate acquisition member. Invarious embodiments, the angular deflections associated with each axisor joint may be configured independently. For example, each axis mayhave a selected angular deflection which provides a limited range ofmotion to the associated arm sections or alternatively each selectedaxis may be configured with substantially infinite range of motionthrough rotatable joint elements. Additional details of the applicationof infinitely rotatable joint elements in CMM design as well as furtherdescription of the various other components associated with coordinatemeasuring devices are described in U.S. Pat. No. 5,829,148 entitled“Spatial Measuring Device” which is incorporated by reference in itsentirety.

It will be appreciated that the aforementioned rotational axes andassociated angular deflections are meant to be illustrative only andthat other axes and ranges of motion may be used which may be more orless restrictive in nature. In one aspect, the combination of differentjoints and their associated angular deflections or ranges of movementprovide for a highly flexible means by which the coordinate acquisitionmember 110 may be positioned and oriented. As previously described, eachjoint may be associated with an articulation member 115 that may beremotely driven via an associated outer member and actuatorinterconnected via a flexible drive cable thereby providing a means forfinely controllable movement and positioning of the measuring arm 105.Further details of how the actuators can be arranged with respect to thearticulation members 115 and measuring arm 105 will be described ingreater detail in subsequent figures and discussion.

FIG. 2B illustrates an exploded view 250 of a portion of the measuringarm 105 shown in FIG. 2A that details the interconnection between thecompliant members or bushings 135 and the inner and outer members 130,132 of the measuring arm 105. In one aspect, the compliant members 135are formed from a resilient deformable material such as soft plastic orrubber which allows positioning of the inner member 130 within the outermember 132. A plurality of such compliant members 135 may be usedthroughout the measuring arm 105 to maintain a desired orientationbetween various arm segments in which the inner and outer members130,132 are substantially aligned along a longitudinal axis 260.

The deformable nature of the material used in the compliant member 135allows for a certain degree of compressibility in the compliant member135 when sufficient force or torque 265, 270 is applied to either theinner or outer members 130, 132. As will be described in greater detailhereinbelow, this quality of deformability serves a number of usefulpurposes which may include imparting a vibration dampening quality tothe measuring arm 105. For example, vibrations which occur in the outermember 132 may not necessarily be transmitted to the inner member 130 byvirtue of the compliant member 135 which at least partially absorbs thevibrations. This feature of the compliant member 135 is useful in thatit acts to buffer the inner member 130 from outside physicalperturbations which might otherwise result in misalignment ormisregistration by the coordinate acquisition member 110.

In a similar manner, the compliant member 135 being interposed betweenthe inner and outer members 130, 132 creates a temperature buffer thatreduces changes in the ambient temperature surrounding the outer member132 and localized “hot” spots created near operating actuators/motorsfrom being transmitted to the inner member 130 to a significant degree.In one aspect, a gap 275 created between the inner and outer members130, 132 by the compliant member 135 serves to isolate the inner member130 from undesirable thermal changes which might occur in or about theouter members 132. Thermal stability is a significant concern inmeasuring arm performance as changes in temperature may result inexpansion or contraction of the arm sections and/or joints and maycontribute to misalignment and deviations from calibrated movement. Inone aspect, the materials from which the compliant members 135 areconstructed also promote thermal stability in the inner member 130 byacting as an insulator to heat transfer. Thus, the exoskeletal structureof the outer members 132 desirably contributes to improved measuring armdata acquisition stability and precision. Furthermore, the exoskeletalstructure used in connection with the measuring arm potentially reducesthe frequency of re-calibration that might otherwise be necessary ascompared to conventional measuring arms operating in similarenvironments.

In certain embodiments, one or more pressure sensors or strain gauges280 may be associated with each compliant member 135. The pressuresensors or strain gauges 280 permit a measurement of the degree ormagnitude of deformation associated with a selected compliant member135. Deformation in the compliant member 135 is generally indicative oftorque, force, or load applied to either the inner or outer members 130,132 relative to one another. Information provided by the pressure sensor280 characterizing the deformation load may be used to supply feedbackdata to a controller which may in turn instruct a preselected movementfunction or operation to be carried out by the actuator based upon thedegree of deformation detected by the pressure sensor 280. For example,the pressure sensors 280 may be used to identify the general location,magnitude, and direction of an external load applied to the outer member130. The controller may respond to the external load by directingselected actuators to drive articulation members 115 to generate an“opposing-force” to resist or compensate for the external load andprevent undesired movement of the measuring arm 105.

In a similar manner, the controller may respond to the detected externalload by directing actuators to drive selected articulation members 115to move in a direction generally “in-line” with the applied load. Theseoperations provide a basis for motor-assisted movement of the measuringarm 105 wherein application of force or load on the measuring arm 105 orthe coordinate acquisition member 110 causes the arm 105 to move at apredetermined rate in a selected direction. As will be described ingreater detail hereinbelow, motor-assisted movement may be desirablyapplied in a “teaching mode” wherein an operator at least partiallydirects the movement of the measuring arm 105 aided by thecontroller-directed actuator movement of the articulation members 115.

In other embodiments, the controller may direct the speed and directionof movement of the measuring arm 105 on the basis of the magnitude ofload applied to the inner or outer members 130, 132 as detected by theone or more pressure sensors 280. Additionally, in certain embodimentsif the inner member 132 experiences a suddenly applied load, such asthat encountered if the coordinate acquisition member 110 is jarred orinadvertently moved from a desired position, the load applied to theinner member 132 or coordinate acquisition member 110 may be detected bythe pressure sensors 280. The detected load may further trigger thecontroller to issue corrective or compensatory feedback to one or moreactuators and associated articulation members 115 to thereby return thecoordinate acquisition member 110 to its previous position. Such afeature is useful to maintain proper alignment and positioning of thecoordinate acquisition member 110 even when accidentally orinadvertently mispositioned.

FIG. 2C illustrates another way to detect the position and alignment ofthe measuring arm components using an encoder-based approach. In thisembodiment, encoders may used to independently ascertain the positionand/or orientation of both the inner and outer members 130, 132 atselected locations about the measuring arm 105. For example, the angulardegree of freedom denoted by the ‘B’ axis may be accurately assessedusing two encoders which evaluate angular values for both the inner andouter members 130, 132 at the selected location. To evaluate the stateof articulation of the measuring arm 105 about this axis, a firstencoder 282 may be used to track the position and/or orientation of theinner member 130 and a second encoder 284 may be used to track theposition and/or orientation of the outer member 132. As will bedescribed in greater detail hereinbelow, the relative position of theinner and outer members 130, 132 may be associated on the basis of thefirst and second encoder angular values 282, 284 wherein the outermember 132 and associated encoder 284 define “course” positioning of themeasuring arm 105 and the inner member 130 and associated encoder 282define “fine” positioning of the measuring arm 105.

It will be appreciated that a number of possibilities exist fordetecting changes in position and/or alignment between the inner andouter members 130, 132. Aspects of the invention as described herein aretherefore conceived not to be limited solely to the use of straingauges, pressure sensors, and/or encoder-based methods for detectingpositional differences between these members 130, 132. Furthermore, incertain embodiments, the aforementioned components for positionaldetection may be used alone or in combination as desired withoutdeparting from the scope of the present teachings.

In one aspect, the aforementioned deformable characteristics of thecompliant member 135 provide a limited range of positioning or alignmentof the inner member 130 with respect to the outer member 132 even whenthe outer member 132 remains fixed in position. Thus, for a selecteddegree of freedom, positioning of the measuring arm 105 may be achievedby actuator driven movement of the outer member 132 wherein theassociated encoder 284 may be used to determine the operation of theactuator and identify when the desired position of the outer member 132has been achieved. Positioning of the outer member 132 directs movementof the inner member 130 such that when the outer member 132 has come torest at a selected position, a state of equilibrium between the innerand outer members 130, 132 is achieved. When so positioned, the encoder282 associated with the inner member 130 may be evaluated to determineits position and alignment relative to the outer member 132. To achievea certain desired position of the inner member 130, the encoder 282associated with the inner member 130 may be used to determineappropriate movements of the outer member 132 necessary to achieve thedesired position. In one aspect, a feedback loop is established whereinthe outer member encoders 284 and inner member encoders 282 operate inconcert to achieve a selected position. Furthermore, these encoders 282,284 may also be used to determine when the measuring arm 105 has becomemisaligned due to jarring, vibration or other physical perturbations andprovide a means to reacquire a selected or desired position.

The dual encoder approach to position and orientation determinationprovides for improved measuring arm performance and accuracy as comparedto conventional robotically assisted articulated CMMs. For each degreeof freedom associated with the measuring arm, a discrete encoder pairmay be used to resolve, monitor, and correct the position and alignmentof the measuring arm 105 within the selected degree of freedom toachieve a highly accurate positioning system. Thus in variousembodiments, individual inner and outer member encoder pairs may beassociated with the ‘A’, ‘B’, ‘C’, ‘D’, ‘E’, ‘F’ and ‘G’ axis (show inFIG. 2A) and various combinations thereof to provide a means toaccurately monitor arm position and alignment about each degree offreedom. Information acquired from each encoder pair may further serveas a basis to drive actuators either singularly or in combination toposition the outer member 132 and thereby align the inner member 130 ina desired position and/or orientation.

In one aspect, the measuring arm 105 provides a self calibrating qualitythrough the interaction of the inner member 130 and associated encoder282 and the outer member 132 and associated encoder 284 where thelocation and motion information provided by each can be analogized toindividual senses and can be used for purposes of “teaching” oneanother. This manner of operation may be analogized to how humansutilize the senses of sight and touch to refine movement when graspingan object.

Numerous different measuring arm/encoder configurations may beimplemented to achieve the desired results of the aforementionedteachings. For example, the encoders 282, 284 associated with the ‘B’axis may be located at substantially different positions from thoseshown in FIG. 2C while still operating in a manner which allows formonitoring and control of the inner and outer members 130, 132. As such,encoder positioning about each axis or degree of freedom is conceived tobe not necessarily limited to the configurations shown and other encoderpositionings are considered representative of embodiments of the presentinvention that may be readily appreciated by those of skill in the art.Additionally, the present invention is not necessarily limited to pairedencoders for each degree of freedom and may incorporate additionalencoders to monitor and direct the positioning of the inner and outermembers 130, 132 thereby potentially improving instrument precisionand/or accuracy. Furthermore, a “composite” encoder capable ofsimultaneously measuring two or more positionings (e.g. both inner andouter members together) may be used as a substitute for the individualencoders 282, 284 associated with the inner and outer members 130,132.

FIG. 3 illustrates an exemplary remote actuator configuration PCMM 100.In this embodiment, the actuators 305 used to drive the variousarticulation members 115 along the measuring arm 105 are housed orcontained within the mobile unit 145. In this configuration, heat andvibration that might otherwise be associated with operation of theactuators 305 is contained within or dampened by the mobile unit 145.The actuator power used to operate the various articulation members 115is further transmitted by the flexible drive cables 155 which areinterconnected between the actuators 305 and the articulation members115. Although illustrated as having a certain degree of “slack” withinthe power transfer cables 155 it will be appreciated that the powertransfer cables 155 may be firmly and securely affixed to varioussections of the measuring arm 105 in such a manner so as to minimizeundesired movement and play within the power transfer cables 155. Thusthe driving force generated by operation of the actuators 305 isefficiently transferred to the articulation members 115 in a controlledand reproducible manner. Alternatively, some degree of slack tolerancewithin the drive cables 155 may be desirable to provide a damping meansfor reflected loads resulting from operation of the actuators 305.Additionally, a flywheel or other inertial damping mechanism may be usedin connection with the actuators 305 and drive cables 155 to offset theeffects of reflected load in the drive cables 155.

In one aspect, the aforementioned actuator configuration 300 desirablyimproves PCMM performance by displacing sources of heat, vibration, andexcess weight away from the measuring arm 105 itself. Additionally, aswill be described in greater detail herein below the actuators 305 maybe used to control movement of the measuring arm 105 and to respond tostimulus and feedback associated with the pressure sensors 280, encoders282, 284 and compliant members 135 located at various positionsthroughout the measuring arm 105. In certain embodiments variousencoders associated with the inner and/or outer members 130, 132 may bepositioned within the mobile units 145 along with the actuators 305.Remotely located encoders are able to ascertain the angular values forthe inner and outer members 130, 132 by directly engaging with theactuators 305 or drive cables 155 or by various other means so as toallow determination of the relative position of the measuring arm 105.

FIG. 4 illustrates another exemplary remote actuator configuration forthe PCMM 100. In this embodiment, actuators 305 used to drive selectedarticulation members 115 are mounted at various positions about themeasuring arm 105 and mobile unit 145. In one aspect, the location ofeach actuator 305 is displaced from the articulation member 115 which itis configured to operate and interconnected via an appropriate length ofdrive cable 155. For example, the articulation member(s) 115 associatedwith the elbow joint 210 may be driven by actuator(s) 410 positionedgenerally about the shoulder joint region 205. In a similar manner, thearticulation member(s) 115 associated with the shoulder joint 205 may bedriven by actuator(s) 415 remotely located near the base 140 of themeasuring arm 105 or alternatively within or upon the mobile unit 145.

In one aspect, displacement of the actuator 305 from the articulationmember 115 is it configured to operate desirably reduces vibrations andlocalized heat buildup in the regions of the articulation members 115.This manner of configuration is distinguishable from that ofconventional CMM's wherein the actuator is integrated with, or locatedsubstantially adjacent to, the articulation member it operates. Suchdesigns are inferior as they may result in localized heating andvibrational instability. Furthermore, the actuators themselves are asignificant source of weight and may increase the overall load requiredto move and position the measuring arm 105. In various embodiments,larger actuators (e.g. those generating the most heat and vibration) areassociated with directing the outer members 132 which drive thearticulation members 115 located about the shoulder joint 205 and it istherefore desirable to locate these actuators 305 some distance awayfrom the measuring arm 105 to reduce physical perturbations includingheat and vibrations as well as reduce the overall weight of themeasuring arm 105. Similarly, actuators 410 used to control the elbowjoint 210 may be smaller than the shoulder actuators 415 and may bedisplaced near or about the shoulder joint 205 without significantlyaffecting the performance of the measuring arm 105. This generalapproach to displacing actuators 305 one or more arm sections away fromthe articulation member 115 they are designated to drive therefore hasthe desirable effect of reducing heat buildup, vibrations, and weightwithin the measuring arm 105. At the same time, this configurationmaintains relatively short lengths of drive cable 155 between theactuator 305 and the outer members 132 and the articulation members 115they drive.

In various embodiments, the actuator displacement distance may beadjusted as needed or desired to accommodate a variety of actuatorplacement configurations. For example, some actuators 305 may bepositioned relatively short distances away from their associatedarticulation members 115. Thus, an actuator 425 used to drive anarticulation member 115 located in the wrist joint 215 of the measuringarm 105 may be located a relatively short distance away from the wristjoint 215 as illustrated or alternatively may be displaced a furtherdistance away from the wrist joint 215 such as along the arm section 430or alternatively near the elbow joint 210. The exact distance that theactuators 305 are displaced from the associated articulation member 115may therefore be configured as desired to reduce vibrations, heatbuildup, and weight while at the same time maintaining a desired lengthof flexible drive cable 155 which insures accurate and efficient powertransfer. From the foregoing, it will be appreciated that many possibleactuator configurations and placement patterns exist which need notnecessarily conform specifically to those illustrated. However,alternative actuator configurations and placement patterns which applythe principals of remote operation between the actuator and articulationmember are considered but other embodiments of the present teachings. Invarious embodiments, the flexible drive cables 155 used to interconnectthe actuators 305 and articulation members 115 may be substituted withother comparable or analogous means for transferring power. For example,rigid or semi-rigid drive cables may be used in place of the flexibledrive cables 155 and may include drive shafts, wires, elongated couplingdevices or other such components.

FIG. 5 illustrates one embodiment of a control diagram 500 detailing theprinciple components of the PCMM 100 that provide for feedback andcontrol of the measuring arm 105. In one aspect, the measuring arm 105can be logically subdivided into a plurality of articulated sections 515representative of selected degrees of freedom of movement within themeasuring arm 105. Movement and/or alignment of the inner and outermembers 130, 132 of the articulated section 515 may be determined usingencoders 282, 284 which provide information that may be used toascertain the position of the inner member 130 with respect to the outermember 132. As previously described, changes in the position oralignment of the inner member 130 with respect to the outer member 132may be observable as a result of the qualities of deformability of thecompliant member 135 which affords a degree of tolerance and moveabilitybetween the two members 130, 132.

For each articulated section 515, a first outer member encoder 284 maybe used to determine the relative position and/or alignment of the outermember 132 and a second inner member encoder 282 may be used todetermine the relative position and/or alignment of the inner member130. The function and operation of encoders is known to those of skillin the art and is described in detail in U.S. Patent No. 5,829,148entitled “SPATIAL MEASURING DEVICE” previously incorporated byreference. In certain embodiments, each encoder 282, 284 providesinformation to a controller 520 which may be configured to ascertain therelative position of the inner and outer members 130, 132 using adatastore or lookup table 525.

The datastore or lookup table 525 associates encoder informationrelating to the position and/or orientation of the inner and outermembers 130, 132 with respect to one another and thereby provides thecurrent and desired positions of these members 130, 132. The lookuptable 525 may further provide information to the controller 520 that isused to direct movement of the articulated section 515 in a desiredmanner based upon acquired information from encoders 282, 284 associatedwith the inner and outer members 130, 132.

The controller 520 receives information from the encoders 282, 284 whichis used to establish the current position and/or alignment of the innermember 130 with respect to the outer member 132. Furthermore, theencoder information may also be used to establish the current positionof the arm 105 in three dimensional space. Based upon this information,the controller 520 directs positioning of the selected components of thearm 105 through actuator-driven movement of the outer member 132 whichin turn directs the positioning of the inner member 130. Additionaldetails of how the lookup table 525 may be constructed and utilized willbe provided in subsequent figures and discussion.

In various embodiments, the controller 520 directs measuring armpositioning at a selected position or degree of freedom by providinginstructions to an actuator controller 530 which in turn directs theoperation of the actuator 305 associated with the outer member 132. Theactuator 305 is capable of positioning the outer member 132 in a desiredposition and/or orientation with a high degree of precision and control,either directly or indirectly through the aforementioned drive cable155. Upon movement of the outer member 132, the inner member 130 ispositioned via the transmission of force through the compliant member135. As previously noted, a significant feature of the present teachingsis the ability to robotically position the inner member 130 using theouter member 132 to provide the driving means without an actuatordirectly operating upon the inner member 130. This configurationprovides for improved control and vibration damping while at the sametime allowing the position and/or alignment of the inner member 130 tobe monitored and adjusted as needed or desired.

In one aspect, the encoders 282, 284 provide the ability to not onlyresolve the current location of the inner and outer members 130, 132 ofthe measuring arm 105 but may also be used to determine alignment,strain, load or other physical parameters associated with the arm 105.While illustrated as having discrete encoders 282, 284 for the inner andouter member 130, 132 it will be appreciated that a singular encoderdevice or multiple encoders may be used for the purposes of identifyingthe position and/or orientation of the inner member 130 relative to theouter member 132. Additionally, for articulated sections 515 havingmultiple degrees of freedom of movement there may be additional controlgroupings (e.g. actuators, actuator controllers, encoders, etc.)contained within the articulated section 515 that operate in concertwith one another.

The controller 520 directs how the selected articulated section 515 willbe positioned based upon a feedback loop wherein a desired position ofthe inner member 130 is identified and actuator instructions areretrieved from the lookup table 525 and subsequently issued to drive theactuator 305 via the actuator controller 530. As the outer member 132 ispositioned by the actuator 305, the encoders 282, 284 may provideinformation to the controller 520 as to the progress of the positioningof the articulated section 515. This information can be used to makecorrections and/or adjustments in the positioning of the articulatedsection 515 or the arm 105 or to determine when the arm 105 has achieveda desired position and/or orientation.

The encoder(s) 282, 284 associated with the selected articulated section515 may be configured to assess the positional state of the inner andouter members 130, 132 and relate this information in terms of angularvalues or cycles of rotation of each encoder 282, 284. Additionally,positional information may be obtained from pressure sensors or straingauges 280 associated with the compliant members 135 between the inner130 and outer members 132 of the measuring arm 105. Using thisinformation, the encoders 282, 284 can be used to effectuate actuatoroperation to achieve a desired position or alignment of the measuringarm 105. For example, the controller 520 may determine that the innermember 130 is misaligned (as a result of jarring or vibrations) on thebasis of increased compression or deformation of a particular compliantmember 135 as indicated by an associated pressure sensor 280.Alternatively, the controller 520 may determine that the inner member130 is out of alignment by evaluation of the information obtained fromthe encoders 282, 284 which may further be used in combination withinformation obtained from the pressure sensors 280.

The encoders 282, 284 may further direct the actuator 305 (through theactuator controller 520 or controller 520) to operate in a manner thatalleviates the compression or deformation of the compliant member 135 ordirects the outer and inner members 130, 132 to a selected position tothereby provide corrective movement of the measuring arm 105 returningit to a desired position. In one aspect, the aforementioned feedbackloop may be used to automatically sense and correct deviations inmeasuring arm position. Additionally, the feedback loop may be utilizedin routine alignment and positioning operations to finely control themovement of the articulated section 515 and measuring arm 105.

In various embodiments, the number of encoders utilized may beassociated with the number of degrees of freedom of movement orrotational axis of the PCMM. For example, each degree of freedom ofmovement of the measuring arm 105 may be evaluated and monitored using asingle inner/outer member encoder pair that may be used to trackpositioning and provide feedback as to deviations and misalignments ofthe articulated sections 515 or measuring arm 105. In other embodiments,additional encoders may be associated with one or more of the identifieddegrees of freedom of movement to provide redundant encoder analysis andfeedback. Incorporation of multiple encoders in this manner may improvethe accuracy of movement tracking by the encoders and provide forincreased positioning sensitivity and accuracy.

The aforementioned manner of identifying, tracking, and effectuatingmeasuring arm position through the use of inner and outer member encoderevaluation improves error mapping and self calibration characteristicsof the measuring arm as compared to conventional measuring arms. In oneaspect, the information contained in the lookup table 525 may bedeveloped using a training program 540. In various embodiments, thetraining program 540 associates encoder/actuator information withpositional information through a plurality of selected positionings ofthe measuring arm 105 for which the encoder/actuator information used toachieve the arm position 105 is identified. This information may serveas a calibration reference to detect and direct the movement orpositioning of the measuring arm 105 by evaluating encoder readings fromthe inner and outer members 130,132 and comparing this information todata stored in the lookup table 525. Additional details of how thelookup table 525 may be created and the training program 540 utilizedwill be described in greater detail hereinbelow.

In various embodiments, the controller 520 may direct the operation ofthe actuator 305 both in terms of speed and duration in order toeffectuate desired angular movements of the selected articulated section515 and also the rate at which the movement occurs. This manner ofcontrol over each articulated section 515 provides for enhancedfunctionality and may be used to direct different modes of operation ofthe PCMM 100.

In various embodiments, a single controller may be associated with aplurality of different articulated sections 515. For example, a singlecontroller may direct and coordinate the motion and alignment of thevarious sections of the measuring arm 105 including the shoulder joints205, elbow joints 210, wrist joints 215, and the coordinate acquisitionmember 110. Alternatively, multiple controllers may be used wherein eachcontroller is associated with one or more selected articulated sections515 and coordinate the movement and positioning of those sections 515alone. Additionally, a “master” controller may be used to direct theoperation and activities of a plurality of independent controllers suchthat the movement and positioning of the arm 105 may be centrallycoordinated.

FIG. 6 illustrates a flowchart 600 for developing a training parameterset for the PCMM 100. The training parameter set comprises informationstored in the lookup table 525 and may correspond to a plurality ofangular values for each degree of freedom of the measuring arm 105 orrotational cycles for each encoder that may be used to achieve theselected angular values. This information may be used to determine thecurrent position of the measuring arm 105 and provide instructions tothe controller 520 associated with each articulated section 515 whichdirect the measuring arm 105 to a desired location. In certainembodiments, the training parameter set provides an error mappingfunctionality that may be used for purposes of self-calibration andadjustment by resolving the current and desired positional information.

In general, the training parameter set defines the characteristics andpositional adjustment parameters associated with a particular instrumentor configuration. These parameters may be applied to similar instrumentsor configurations such that the parameters developed for one instrumentmay be used to train or clone another instrument. The portable nature ofthe parameter set desirably provides a means to calibrate multipleinstruments in a more efficient manner than by calibrating eachinstrument independently of one another.

In one aspect, the training parameter set represents a relatively largenumber of values relating to a collection of articulations of themeasuring arm 105 in three dimensional space. This information maycomprise between approximately 100-10000 different articulations of themeasuring arm 105 and the corresponding encoder values relating to thesearticulations. Consequently, it is desirable to provide the ability to“share” this information between different instruments such that thetraining parameter set need only be developed on a first instrument.This feature improves the speed with which instrument calibrations maybe performed in subsequent instruments and represents a significant timesaving feature. Of course, it will be appreciated that the trainingparameter set need not necessarily be shared between instruments and canbe developed independently for each instrument.

The development of the training parameter set commences in state 610wherein instructions for positioning the measuring arm 105 in a selectedlocation and orientation are identified and issued to the controller 520to effectuate the desired movements of the outer member 132 which inturn aligns and positions the inner member 130 as previously described.In one aspect, these instructions relate to specified angular values foreach degree of freedom of the outer member 132 and/or encoder cyclesassociated with the encoders 284 and actuator controllers 530 of theouter member 132.

Once positioned according to these instructions, the actual location andorientation of the inner members 130 of the measuring arm 105 aredetermined in state 620. This information may include the valuesassociated with the encoders 282 of the inner member 130 for eacharticulation member 515 as well as geometry information acquired by theprobe 110 which identifies its location in three dimensional space.Thus, the training parameter set associates a collection of outer memberencoder values with a corresponding collection of inner member encodervalues. As will be described in greater detail hereinbelow thisinformation desirably provides a means to not only direct a desiredpositioning and alignment of the measuring arm 105 but also to resolvethe current position and alignment of the measuring arm 105 on the basisof the stored encoder values.

In state 630, entries in the lookup table 525 are populated byassociating each set of encoder values for the outer members 132 (e.g.for each axis, degree of freedom, or join member) with encoder valuesfor the inner members 130. In this manner, encoder values orinstructions for actuator assisted positioning of the measuring arm 105via the outer member 132 may be determined to achieve a plurality actualmeasuring arm locations.

Stored entries in the lookup table 525 may be subsequently accessed bythe controller 520 to effectuate accurate and precise movement of themeasuring arm 105. For example, when the measuring arm 105 is to belocated in a selected position and orientation, the controller 520 mayaccess an appropriate entry in the lookup table 525 corresponding to thedesired location (specified by the inner member encoder values) anddrive the actuators 305 associated with the outer members 132 to achievethe corresponding outer member encoder values. Utilization of the lookuptable 525 in this manner therefore provides a deterministic means toposition the arm in a robotically controlled manner without the need tomanually “guide” the arm to a desired location.

As each entry in the lookup table 525 relates to a singular position ororientation of the measuring arm 105 a plurality of such entries isdesirably determined to define a range of potential measuring armarticulations that may be accessed to position the measuring arm inthree dimensional space. Thus, to generate a “complete” lookup table 525one or more additional operations 610, 620, 630 may be performed asillustrated by decision state 640.

In one aspect, lookup table entries determined according to theaforementioned steps may be iteratively performed by the trainingprogram 540 which specifies a series of outer member encoder values tobe associated with corresponding inner member encoder values when themeasuring arm 105 is positioned or oriented. For example, the trainingprogram 540 may specify a collection of outer member encoder values inwhich each axis or degree of freedom of the measuring arm 105 ispositioned a pre-selected amount and the associated inner member encodervalues corresponding to these positions is determined and stored in thelookup table 525. In various embodiments, increasingly large numbers ofentries in the lookup table 525 improve the “resolution” of positioningthe measuring arm 105 and may comprise between 1000-10000 entries toprovide relatively high resolution in a seven axis measuring arm system.In various embodiments, the use of the training program 540 desirablyalleviates the need for an operator to manually position the measuringarm 105 when populating the lookup table 525 however it will beappreciated that manual selection and determination of lookup tableentries may also be performed as desired.

In certain embodiments, training parameter entry determination may beperformed multiple times for selected locations to establish correctionfactors, offset values, or variability ranges which may be also storedin the lookup table 525. In this manner, the lookup table 525 may berefined and validated prior to use or dissemination to otherinstruments.

Once development of the training parameter set and lookup table 525population is complete (state 650), this information may be re-used as areference for other similar instruments. For example, as shown in state660, a comprehensive training parameter set may serve as a basis forcloning other instruments wherein the lookup table 525 is accessed by asimilar instrument without redeveloping the entire contents of thetraining parameter set and lookup table 525. In this fashion, subsequentcloned instruments may be more rapidly calibrated as they are able tomake use of the existing training parameter set.

The time saving aspect of lookup table 525 development and trainingparameter portability can be readily appreciated when the number ofindividual calibration points used for instrument calibration is large.For example, it is not uncommon for between approximately 1000-10000individual calibration points to be used during instrument calibration.Training parameter set development need only be performed once howeverand this information may be shared between similar or compatibleinstruments thus alleviating the need to re-perform these operations foreach instrument. Such a manner of calibration is a notable improvementover existing or conventional methods which require each instrument tobe individually calibrated.

In an analogous manner other instructions or parameter sets may bedeveloped and cloned into similar or compatible instruments. Forexample, error correction parameters, physical perturbation adjustments,and other defined measuring arm movements and positionings may beestablished on a reference instrument and the parameter set used to“teach” other instruments alleviating redundant determination of theinstructions or parameter set.

Application of the aforementioned principals in the context of CMM andPCMM instruments can be expected to markedly improve measuring armpositioning accuracy and precision as compared to many conventionaldevices. In various embodiments, the sensitivity of a measuring armemploying an encoder driven outer member structure can result insensitivity on the order of approximately 10-50 microns or better.Additionally, the reproducibility of measuring arm positioning issuperior to conventional systems resulting in part from the feedbackloop created by the inner and outer member encoders 282, 284 as well asthe use of the lookup table 525 for purposes of directing the actuators305.

FIG. 7 illustrates an exemplary lookup table entry 700 that may begenerated and utilized as described above. In one aspect, the lookuptable 525 comprises a plurality of such entries 700 which relate outerand inner encoder values 705, 710 for each axis or degree of freedom 715of the measuring arm 105 based upon a selected position and/ororientation of the measuring arm 105.

Each entry 700 may comprise information in addition to the encodervalues 705, 710 which may include for example: a gear ratio 720associated with the outer member for each axis 715, an outer memberencoder resolution 725 and an inner member encoder resolution 730(illustrated as cycles per revolution of the encoder), and anapproximate articulation angle 735 for each axis of the outer member 132based upon the specified encoder values 705. This information inaddition to the encoder values 705, 710 may be used for a variety ofpurposes including performing interpolation operations to identifyappropriate encoder and actuator positionings that may be used toachieve measuring arm positions or orientations that are not found inthe lookup table 525. In such instances, a best fit or closest matchapproach may be used to identify suitable actuator movements based uponexisting information contained in the lookup table 525.

It will be appreciated that the aforementioned table entry 700represents but one embodiment of the type of information that may bestored in the lookup table 525. The nature of the contents of the lookuptable 525 may deviate somewhat from that illustrated while stillachieving similar results in relating inner and outer member encoderpositions or values. In general, the lookup table 525 serves to not onlyprovide a means to determine the appropriate positioning of themeasuring arm 105 but may also be used to ascertain the current positionof the measuring arm 105 on the basis of the actuator information.

Additionally, the interpolation operations may identify two or moreentries 700 in the lookup table 525 and use the information containedtherein to develop a new entry which may be stored in the lookup table525 and used to position the measuring arm 105. These extrapolationoperations therefore may be used to not only position the measuring arm105 but also create the potential for a dynamic or evolving lookup table525 which may incorporate additional entries beyond those initiallyidentified during training parameter development.

In various embodiments, the aforementioned robotic measuring system 100may be configured to operate in an assisted-movement mode or“joystick-enabled” mode. In this mode of operation, positioning of themeasuring arm 105 may be accomplished by an operator who guides theapparatus in various desired directions and/or orientations by exertingpressure or force upon portions of selected inner members 130. In oneembodiment, the system 100 is configured to detect and be responsive torelatively slight movements of the inner member 130 without requiringthe operator to exert a force sufficient to move the entire measuringarm 105 and associated hardware components. A high level of sensitivityis achievable in detecting movements or changes in position of the innermember 130 as a result of the deformable characteristics of thecompliant member 135 and the position detecting means of the pressuresensors, strain gauges, and or encoders as described above.

For example, a slight manually-exerted force upon selected inner members130 may be detected by the system 100 which may ascertain both therelative amount of force applied and direction of movement against thecomplain member 135. The system 100 may respond with selectedactuator-driven movements of the measuring arm 105 in the generaldirection and orientation of the manually exerted force providing meansfor the operator to “guide” the movement of the measuring arm 105 withrelatively little effort.

Guided movement or positioning of the measuring arm 105 in theaforementioned manner may be accomplished by controller-based monitoringof the position and orientation of the measuring arm 105 usinginformation provided by encoders, pressure sensors, and/or straingauges. In one aspect, the controller 520 may detect an exerted forceupon the measuring arm components based upon a change in position and/ororientation of the inner members 132 from an established or staticposition. The magnitude of the exerted force used to initiateassisted-movement may be configured as desired and may be relativelysmall, wherein only a slight movement of the inner member 130 withrespect the outer member 132 is needed to effectuate a degree ofrobotically driven movement.

In one exemplary configuration, an operator may exert a force against aselected section of the inner member 132 in a desired direction. Thisforce need not necessarily be large enough to move the entire measuringarm 105 but rather be sufficient to result in some degree of movement ofthe inner member 130. The controller 520 may be configured to discernthe relative direction of the exerted force based upon what support webs135 are deformed and/or the change in position of the inner member 130with respect to the outer member 132 (as detected by the encoders,pressure sensors, and/or strain gauges). Upon determination as to thedirection of the exerted force, the controller 520 may instructappropriate actuators 305 to direct movement of the measuring arm 105 ata pre-selected rate of speed and/or distance for a selected period oftime or until the exerted force is no longer detected. Based on thisprincipal, manually-guided movement of the measuring arm 105 can beaccomplished to facilitate manual positioning of the measuring arm 105in such a manner so as to significantly reduce operator fatigue andeffort in aligning and calibrating the instrument 100.

In various embodiments, a selected threshold level of exerted force ordetected movement may be required to initiate the assisted-movementmode. Likewise, the magnitude of the exerted force or detected movementmay be assessed to determine the characteristics of theassisted-movement to be used (e.g. speed, duration, distance,orientation, etc.). In still other embodiments, changes in position ofthe various measuring arm components which fall below the thresholdlevel may be perceived as perturbations which may be corrected for byissuing compensatory instructions to selected actuators 305 to realignor position the measuring arm 105 in a desired manner to offset thedetected perturbation(s).

In addition to providing assisted-movement of the measuring arm 105, thecontroller 520 may also be configured to resist movement and maintaincurrent positioning of the measuring arm 105. For example, the operatormay desire the measuring arm 105 to retain a selected position orcompensate for undesired movement of the measuring arm 105. Toaccomplish this, the controller 520 may be configured to maintain aselected positioning and/or orientation of the measuring arm 105 andactively resist applied or exerted force against the various measuringarm components through application of an actuated controlled“counter-force ”. Deviation of the measuring arm 105 from a desiredposition may also be corrected by the controller 520 which utilizes thelookup table 525 to return the measuring arm 105 to the desiredposition.

From the foregoing description it will be appreciated that the measuringarm 105 may be positioned and oriented in a number of different waysincluding substantially autonomous modes wherein the measuring arm isrobotically positioned as determined by the controller 520.Additionally, the measuring arm 105 may be positioned in asemi-automated or manually assisted mode in addition to conventionalmanually operated modes without robotic assistance. Taken together thefeatures and functionalities of the system as described by the presentteachings provide a number of significant improvements over conventionalarticulated measuring arm configurations. In particular, roboticallycontrolled and/or assisted movement of the measuring arm 105 providesthe potential for improved accuracy and precision in acquisition ofcoordinate data.

It will be further appreciated that the positioning and alignmentdetection means in which an inner arm member is driven by an outer armmember may be adapted for purposes other than coordinate dataacquisition. It is conceived that configurations employing anarticulated arm having a instrument, tool or other component that is tobe finely positioned may be adapted to for use with the presentteachings to provide improved response, control, and accuracy in usingthe tool or other component. For example, in surgical applications aconventional metal or laser scalpel may be adapted for use with ameasuring arm wherein the positioning and alignment system of thepresent teachings provides accurate orientation and manipulation of thescalpel such that surgical procedures can be performed in an autonomousor semi-autonomous manner with a high degree of precision.

Although the above-disclosed embodiments of the present teachings haveshown, described, and pointed out the fundamental novel features of theinvention as applied to the above-disclosed embodiments, it should beunderstood that various omissions, substitutions, and changes in theform of the detail of the devices, systems, and/or methods illustratedmay be made by those skilled in the art without departing from the scopeof the present invention. Consequently, the scope of the inventionshould not be limited to the foregoing description, but should bedefined by the appended claims.

All publications and patent applications mentioned in this specificationare indicative of the level of skill of those skilled in the art towhich this invention pertains. All publications and patent applicationsare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference.

1. A positioning system comprising: an articulated supporting arm comprising a plurality of jointedly interconnected support arm segments moveable about a plurality of axes; a plurality of compliant members positioned on said supporting arm; and an articulated measuring arm comprising a plurality of jointedly interconnected measuring arm segments capable of a plurality of degrees of freedom of movement and supported by said compliant members wherein said compliant members provide a yielding characteristic between the articulated supporting arm and the articulated measuring arm.
 2. The positioning system of claim 1 further comprising: at least one alignment detector configured to detect the alignment between the articulated supporting arm and the articulated measuring arm.
 3. A positioning system comprising: a means for providing an articulated supporting arm; a means for providing an articulated measuring arm; a means for providing a yielding coupling between the articulated supporting arm and the articulated measuring arm. 